Dutch Naval Dirk. Comment and help

[Dmitry]

Originally Posted by Atlantia

What would you do about that crack then?

Nothing. You will only make it worse, because you won't be able to match the color, finish and texture of the handle with whatever filler material you will use. A professional restorer should be consulted, although I would just leave it be.
Numbers on the guard indicate it was issued to a graduating cadet. It's a Model 1880. Imho your dirk dates comfortably into the 20th c.
Just a guess - the tulip at the ricasso may indicate Dutch manufacture as opposed to the German.